In magnetic recording (MR) systems, data is typically recorded on concentric circular tracks on a magnetic media as a sequence of small magnetic domains. Data written onto the tracks that neighbor a given track will affect the signal read back from the media of the given track. The signal induced during the read of the given track as a result of one or more neighboring tracks is referred to as crosstalk or inter-track interference (ITI). The mitigation of the ITI noise caused by the neighboring tracks in the read back signal of the given track typically relies on cancellation data based on the data pattern from the neighboring tracks. The cancellation data is typically supplied to an ITI mitigation circuit or process as the given track is being read from the magnetic media. The neighboring tracks may be, for example, logically to the left and right of the given track.
ITI is of particular concern in hard disk drives (HDD) where concentric or spiral tracks of data are recorded on the media in close proximity to one another, relative to the size of the read head. The capacity of the disk drive is increased by placing the tracks closer together. ITI is known to increase with technology scaling, however, and becomes a significant source of noise as track separation distances become smaller. As the tracks are placed closer together, the neighboring tracks are more likely to influence the signal of the given track when it is read back from the media, reducing the overall signal-to-noise ratio. ITI thus limits the number of tracks that can reliably be stored in a given area of a magnetic medium. ITI is of even greater concern in Shingled Magnetic Recording (SMR) systems, where the tracks are placed close enough that the tracks touch one another in some cases and in other cases can even overlap one another when written with data.
A number of techniques have been proposed for mitigating the effect of ITI in magnetic recording systems. In existing SMR implementations, for example, the mitigation process is typically performed by software in the hard disk controller (HDC). It has been found, however, that when ITI mitigation is enabled, the HDC cannot process data fast enough to recover more than one sector of data for multiple revolutions of the disk. Each revolution of the disk, however, may contain, for example, 500 or more sectors of data (depending on, e.g., the particular disk drive that is employed, the size of the disk and the radial position of each track on the disk).
U.S. patent application Ser. No. 13/250,246, filed Sep. 30, 2011, entitled “Hardware-Based Methods and Apparatus for Inter-Track Interference Mitigation in Magnetic Recording Systems,” mitigates ITI by providing ITI cancellation data during a read operation to an ITI mitigation circuit using a write data path of a read channel in the magnetic recording system. The ITI cancellation data can be obtained, for example, from an external memory. While the disclosed ITI mitigation techniques effectively reduce ITI in such magnetic recording systems, a need remains for ITI mitigation techniques that store the ITI cancellation data within the read channel.